1. Field of the Invention
The present invention relates to a fine resist pattern forming method capable of forming an LSI circuit pattern containing a nanoimprint pattern and an ultrafine pattern of several tens nm or less by one imprint process on a wafer and a nanoimprint mold structure for the same.
2. Related Art
A lithography technique for forming an ultrafine pattern has made advances to shorten the wavelength of an exposure light source thereof and provide a high NA of a projector lens and now can form a pattern having hp (half pitch) of about 45 nm with a wavelength (ArF) λ=193 nm in the following expression.Resolution=k1×λ/NA However, the resolution limit of an ArF immersion exposure technology is considered to be within hp 35 nm to 39 nm. Therefore, at present, there is no lithography tool capable of mass-producing an LSI at the hp 32 nm or less as a post ArF immersion exposure technology.
On the one hand, of the exposure tools promising for practical use, an attention has been drawn to nanoimprint technology and nonadiabatic near-field light exposure technology as a technique for providing a high resolution with lowest cost. Nanoimprint is a technique for patterning by pressing a template referred to as a mold against a resin and can faithfully transfer a fine pattern formed on a mold surface. However, the degree of technical difficulty is extremely high in that a mold pattern needs to be formed with a high precision because the mold pattern is of the same size as the transfer pattern.
On the other hand, an attention is drawn to a nonadiabatic near-field light exposure technology as a technique for forming an ultrafine pattern. According to the nonadiabatic near-field light exposure technology, a photomask on which a pattern is formed on a glass substrate with a conductive material is provided in proximity to a surface of a resist deposited on a substrate surface; when a nonresonant light (light having longer wavelength than that of light corresponding to a resonance energy between molecules constituting a resist film) of a wavelength band other than the photosensitive band of the resist is irradiated onto the resist, surface plasmons are generated around an edge portion of a light shielding conductive film by near-field light (including evanescent light) and an adjacent resist portion is exposed to light. To date, experiments using a G line (λ=435 nm) and i line (λ=365 nm) as excitation light have confirmed that a pattern can be formed on the order of a minimum 10 nm.
However, when an LSI pattern is considered, both an ultrafine pattern and a large scale pattern need to be formed, but in general, the nonadiabatic near-field light exposure technology cannot support various pattern sizes because a pattern thereof is formed by surface plasmons around a pattern edge portion (Japanese Patent Laid Open No. 2005-328020). Another method has been proposed in which excitation light is irradiated from the substrate side to which a pattern is transferred and a transfer size is controlled by plasmons on a surface of a convex portion of a mask pattern (Japanese Patent Laid Open No. 2006-269936). Unfortunately, the method has the same problem as the nanoimprint mold fabrication because the process size of the mask pattern needs to be ultrafine. A still another method of combining nanoimprint and nonadiabatic near-field light exposure technology has been proposed in which both side portions of a pattern formed by nanoimprint are exposed to near-field light and the resist is dissolved by development and the pattern is slimmed by dry etching. Unfortunately, the method also has a problem in that the pattern pitch cannot be miniaturized even by the effect of nonadiabatic near-field light exposure because the minimum process size depends on the mold process size (Japanese Patent Laid Open No. 2006-287012).